X-ray apparatus



W. D. COOLIDGE X-RAY APPARATUS.

APPLICATION FILED JULY Is. 1918.

1,365,638. Patented Jan. 11,1921.

inventor: Wiiliam D.Coo|idge b fllfi M 3 His Attorneg.

Original application filed April 13, 1917, Serial No. 161,892. Patent No. 1,810,061.

application filed July 15,

UNITED s'm'n'as WILLIAM D. COOLIDGE, OF SOHENECTADY, NEW YORK, ASSIGNOR T0 GENERAL TRIG COMPANY, A CORPORATION OF NEW YORK.

PATENT OFFICE.

ELEC- X-RAY APPARATUS.

T 0 all whom it may concern Be it known that I, WILLIAM D. Coonmon, a citizen of the United States, residing at Schenectady, in the county of Schenectady, State of New York, have invented certain new and useful Improvements in X-Ray Apparatus, division of my prior application,,Serial 0. 161,892, filed April 13, 1917 patented July 15, 1919, No. 1,310,061,) of which the following is a specification.

The present invention comprises an X ray device having a number of novel features rendering it particularly suitable for operation by people who have little special training in the operation of X-ray apparatus.

Among the novel features of my invention, I desire to call attention to the following:

The X-ray tube is connected directly to the secondary winding of a transformer which all is designed to furnish current at voltages high enough for X-ray purposes, when the primary winding is supplied with alternating current of ordinary. commercial voltage and frequency. To avoid damage to the apparatus by a momentary high voltage which would occur were the circuit closed on thepeak of a current wave, a starting resistance is provided in the primary transformer winding, together with means for eliminating the same.

The Xray tube is so proportioned that the operating current is determined largely by the electric field in the tube instead of being dependent mainly on the cathode temperature as in thermionic X-ra tubes now in use. The filament constituting the cathode or. the X-ray tube is heated to incandescence by current from a transformer, or motor generator, supplied with energy from the same alternating current source, as the h1gh potential transformer connected to the X-ray tube electrodes. This filament supply device may be provided with means for compensating for the initial drop in voltage occurring when the X-ray tube takes current. A terminal common tothe X-ray tube, the main supply transformer and the cathode lighting transformer is connected to ground to reduce the danger of electric shock.

The novel features of my invention will be pointed out with greater particularity in the appended claims and more fully described in the following description taken in connection with the accompanying drawing Specification of Letters Patent.

Patented Jan. 11, 1921.

which is a diagram illustrating a system of connections embodying my invention.

Referring to the drawing, the X-ray tube comprises an envelop 1 consisting, for example, of glass, into which are sealed a cathode 2 and an anode 3. The cathode comprises a coiled filament consisting of highly refractory metals, such, for example as tungsten,

and a surrounding focusing device having a hemispherical member and a cylinder member, preferably also consisting of refractory metal, for example, molybdenum or tungsten. The cathode and the focusing member are electrically connected by-attachin the end of the cathode to the focusing mem or. Two wires 5 and 6 which are connected to the focusing member, together with a wire 7 cathode is positioned, as by bending the wires 5, 6 and 7, or in any other way, to intercept on the focusin member, any inverse discharge taking p ace from a heated focal spot on t e electrode 3 when negative with re spect to the electrode 2. this manner an inverse thermionic discharge is prevented from impinging on the opposite glass wall and injuring the tube. The anode 3 of the X-ray tube consists preferably of wrought tungsten and is connected to an iron tube 11 carried by a lass stem of the tubular extension 12 of the ray tube. Connection is made to an external metal cap 13 provided with ,a ring so the electrical connection may be easily made.

As more fully described in my Patent No. 1,203,495, issued October 31, 1916, the Tat-ray tube is thoroughly freed from gases and exformer 16. The primary of the transformer is [connected by conductors 17 and 17' to a source of alternating current as represented he tube is by conductors l9 and 20. The current through the tube may be indicated by a suitable milliammeter 18.

A current for maintaining the cathode able resistance 24: for regulating the cathode,

heating current. The conductor 15 preferably is grounded as indicated in the drawing. p

The current throughtheX-ray tube depends mainly on three factors, namely, the electron emissivity of the cathode; the tube design; and the impressed voltage. I

In accordance with my invention the tube is designed so that the current limiting effect of the negatively charged cathode focusing member upon the electrons emitted by the cathode is relatively high The cathode filament is operated at such a high temperature that more than sufficient electrons are provided to carry the current, as determined by the geometric construction of the tube and the secondary voltage of the transformer 16. Therefore, with a fixed operating potential slight changes of cathode temperature have little effect upon the amount of operating current through the tube, as

the current is largely governed by the electrostatic conditions within the tube, or what is knownas space charge conditions.

However, as a very substantial drop in voltage occurs in the mains 19, 20, when the tube is taking current from the main transformer 16, means is provided for maintaining the voltage of the filament heating cur rent substantially constant under these conditions to prevent any material change in the temperature of the-cathode. One way for compensating for this drop in voltage comprises a boosting transformer 25, the

primary of which is in series with the primary ofthe main transformer 16 and the secondary of which is connected by conducmade at the peak of a current wave, there would occur a substantially highervoltage' impulse due to the rapid change of magnetization in the transformer. As the transformer and the tube are preferably designed to operate only at more nearly normal voltage, a resistance 28 is provided which is first included in circuit by the closure of the switch 29. This resistance may be removed from "circuit" immediately and the tube operated directl from thealternating current source. or this reason a hand or foot switch may be arranged to close the circuit through the resistance and to automatically eliminate the same by moving the switch to its final closed position.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. The method of operating an'X-ray apparatus comprising an incandescent cathode X-ray tube directly connected to the high potential windingof a step-up transformer which consists in initially applying a current less than the normal operating current to prevent a sudden change of magnetization of the transformer with an accompanying momentary high voltagev impulse and then increasin the current to normal.

2. The method 0 operatingan X-ray apparatus comprising an incandescent cathode'X-ray tube conductively connected to the high potential winding of a step-up transformer which consists in increasing the impedance of the primary transformer circuit during a starting period above a nor- I mal operating value and immediately reduc- WILLIAM D. COOLIDGE. 

